(1) Field of the Invention
The present invention relates to a system for continuously deodorizing and cleaning gas that contains offensive odor ingredients.
(2) Description of the Prior Art
Conventionally, adsorption methods using activated carbon or cleaning methods using a strong oxidizing agent have been typically used for removing sulfur compounds, which are known to be difficult to decompose.
Unfortunately, deodorizers such as activated carbon that have been conventionally used have very low adsorption capacities, with the result that they are ineffective against various offensive odor ingredients. Also, the use of an oxidizing agent requires great skill to accurately match the amount of oxidizing agent used to the concentration of the offensive ingredient.
Gas generated in a sewage treatment plant, a night soil treatment plant, or the like, widely varies in concentration and emits a composite odor. Accordingly, such conventional deodorizers as described above are not suitable to deodorize such malodorous gas. Thus another approach to deodorization has been desired.
In view of the above, various methods for treating foul-smelling gas were proposed. For treating the composite gas discharged from a night soil treatment plant, for example, an oxidizing method using a mixture of a sodium hypochlorite solution and a sodium hydroxide solution, an adsorption method using activated carbon, or the combination of these two methods has been used widely. However, the adsorption treatment with activated carbon results in the maintenance cost being so high that it is often impractical. A sodium hypochlorite solution generally deteriorates over time, rendering its long-term storage difficult. Also, use of the solution requires great skill to accurately control the proper solution to match the concentration of the malodorous ingredient of the gas. Further, the gas emitted from a sodium hypochlorite solution itself contains an offensive and irritating ingredient, which often causes secondary environmental pollution.
In addition, a considerable amount of foul odor remains in the gas treated by the above mentioned proposed method, which means a high fume stack is required to widely diffuse the gas discharged therefrom.
Accordingly, it has been highly desired to develop a method for efficiently deodorizing and cleaning offensive odor ingredients that are hard to decompose by a low-cost method that does not use activated carbon or an oxidizing agent.
In particular, in order to treat malodorous gas at a high removal rate without causing secondary offensive ingredients emitted from a sodium hypochlorite solution to remain in the treated gas, it is necessary to accurately control the amount of treatment chemical corresponding to the wide variation of the initial concentration of the malodorous ingredient. However, such control is not only impractical, it is frequently necessary to replace the treatment chemical.
In order to stabilize the concentration of gas after treatment and to prolong the serviceable time of the adsorbent such as activated carbon or the like, it would be possible to increase the amount of the adsorbent to be filled. However, it fails to decrease the cost of the adsorbent, because the adsorption is carried out in a physical manner. Also, it increases the pressure loss in proportion to the amount of filled adsorbent leading to an increase in operation cost, resulting in failing to improve the maintenance.
Moreover, composite malodorous gas varies greatly in its concentration and composition depending on the time of the year, so that the conventional treatment methods fail to accommodate such variations of composite gas.